On November 9, 2025, tsunami alert in Japan today in Iwate: only waves of 10 to 20 cm were measured in several ports. An episode monitored and closed in three hours, without victims, reminds us of a vigilant archipelago. And it is distinct, by nature and magnitude, from the 2011 earthquake.
On November 9, 2025, at 5:03 PM (JST, 08:03 UTC) at the first hour, an underwater earthquake shook off the coast of Iwate, on the Sanriku coast. The JMA revised it to magnitude 6.9 (USGS 6.8) and triggered a tsunami advisory. Small waves, 10 to 20 cm, hit Miyako, Ofunato, Kuji, and Kamaishi. Alert lifted after three hours, no victims; a reminder of an active seismic zone, distinct from 2011.
What we know at this stage
An underwater earthquake was recorded on November 9, 2025, at 5:03 PM (JST) off the northeast coast of Japan, facing Iwate (region of Sanriku). The Japan Meteorological Agency (JMA) initially assessed the magnitude at 6.7, before revising it to 6.9. Meanwhile, the USGS in the United States placed it at 6.8 — a classic discrepancy, due to different calculation methods and successive updates of seismological parameters.
Following this, the JMA issued a tsunami alert in Japan announcing possible waves up to 1 m in some areas of the Iwate coast. Modest heights were then recorded in several ports: 10 cm in Ofunato, up to 20 cm in Kuji and again in Ofunato, with waves also observed in Kamaishi and Miyako. No deaths or major damage were reported in the early evening. Additionally, no anomalies were detected at the region’s nuclear power plants.
The tsunami alert in Japan was lifted shortly after 8 PM (JST), about three hours after the earthquake. Public media and local authorities broadcast calls to move away from the shore. This continued throughout the alert. The reported disruptions remained limited, including infrastructure checks and temporary halts of railway lines. Furthermore, port inspections were conducted. At the same time, communities urged people to avoid coastal areas and river mouths.
An alert triggered and then lifted: the protocol in action
In Japan, the first minutes following an underwater earthquake are crucial. As soon as the waves are recorded, the JMA compares the probable location, depth, and magnitude, then immediately issues a graded alert message (advice, advisory, alert depending on expected heights). This cycle was applied without delay: message dissemination and display on televisions. Additionally, alert applications relayed the information. Instructions were repeated by municipal loudspeakers along the coasts. The first arrivals were reported around 5:37 PM in Miyako, followed by measurements in neighboring ports. Observing weak waves and no amplification, the JMA lifted the advisory after about three hours.
This well-rehearsed mechanism sets a now-familiar scene: residents move to higher ground, vehicles divert from exposed areas, fishermen check their moorings. This collective reflex results from a risk culture shaped by history. Moreover, this culture is supported by regular drills.
Why the Sanriku coast is on the front line
The coast of Iwate, indecisive and jagged, forms what geographers call a ria coastline: a succession of deep inlets and drowned valleys. This morphology can locally amplify tsunami waves depending on the orientation of the bays. Add to this Japan’s position on the Pacific Ring of Fire, at the junction of several tectonic plates (Pacific, Amur, Okhotsk). Earthquakes are frequent here, sometimes shallow, and some — as we remember — devastating.
The JMA indicated that the event of November 9, 2025 was not directly related to the 2011 earthquake. Let’s recall it in one sentence: on March 11, 2011, a magnitude 9.0 off the Tōhoku coast caused a deadly tsunami and the Fukushima Daiichi accident, resulting in over 15,000 deaths and a long string of industrial and social consequences. Nothing like that here: we are facing a strong but common earthquake on the scale of the archipelago, and the observed waves remained weak.
Magnitudes, discrepancies, and caution: what the numbers mean
Why 6.9 on one side and 6.8 on the other? Magnitude is not a single, fixed measure. Depending on the algorithm (moment magnitude, surface, local), the input data influence the measurement. Indeed, the network of stations and regional corrections, as well as the depth considered, lead to slightly different values. Agencies revise their estimates as new stations are integrated and models stabilize. Hence the importance of indicating the source and dating the version.
Similarly, wave heights differ from one port to another. A wave of 10 to 20 cm does not convey the "real danger" without context: a narrow bay can exacerbate a modest oscillation, an outgoing current can flatten it. For residents, the determining factor is not the precise value. Indeed, the ongoing alert and the associated instruction are crucial. They must stay away from the water and move to high areas until the official lifting.
Instructions and local reactions
In Iwate, the prefectural authorities and municipalities emphasized simple caution: leave the shore, do not go to film the waves, follow live via NHK and municipal channels, and avoid river mouths and estuaries where oscillations concentrate. Transport experienced occasional slowdowns during checks of decks, tunnels, and catenaries.
Most ports suspended maneuvers. Some schools and reception centers briefly opened to shelter residents who moved to refuge areas. These ordinary gestures reflect a prepared country: signage to high points, sirens tested, instructions displayed in stations and on platforms.
Aftermath: monitoring aftershocks, without dramatizing
As often after an earthquake of this intensity, aftershocks may occur in the hours or days following. They do not predict a larger event but can surprise and weaken some already stressed structures. Authorities recommend securing heavy objects. Additionally, it is important to check evacuation routes. It is also necessary to avoid unstable cliffs or dikes that may shift.
From a forecasting perspective, the JMA continues to broadcast tsunami forecasts, bulletins, and height maps; the USGS and regional centers (PTWC) refine the location and kinematics of the rupture. For the public, the challenge is less about following numbers than adopting clear routines. The phone that vibrates, the voice advising to move to higher ground: these are signals that must be recognized without hesitation.
A country accustomed to risk, patient resilience
The Japanese are often credited with a cold discipline; what is seen is a collective learning, sponsored by communities, schools, and businesses. Resilience is not an abstract word: it is the memory of rebuilt villages, raised dikes, maintained footbridges, the care given to evacuation routes.
